This invention relates to a packaging material for photographic photosensitive materials usable for packaging a roll or sheets of photographic film or photographic paper having a sharp edge and a weight of not less than 500 g, and a light-shielding bag formed of it.
A conventional packaging material for photographic photosensitive materials for forming a light-shielding bag is a laminated film having an optical density of not less than 7.5 and a layer construction of PET film layer/adhesive layer/aluminum foil/PO resin layer containing light-shielding material and nonionic antistatic agent in the order from the outside, as disclosed in Japanese Patent KOKAI No. 56-161948. The packaging material is inferior not only in sealability due to insufficient heat sealability but also in physical strength, such as tear strength and impact puncture strength, resulting in the occurrence of bag rupture to lose light-shielding when containing sheets of photographic film having sharp edges without using a pad or a roll of photographic photosensitive material having a weight of not less than 1 kg.
Another conventional packaging material for photographic photosensitive materials comprises, as disclosed in Japanese Patent KOKOKU No. 2-2700, a light-shielding film containing L-LDPE resin in an amount not less than 50 wt. % of the oral polyethylene polymers and not less than 1 wt. % of light-shielding material. The packaging material is excellent in physical strength and heat sealing properties, but is occasionally ruptured by cutting or abrasion caused by dropping or repeated shaking a sealed package containing sheets or a roll of photographic film, photographic paper or the like having sharp edges and a weight of not less than 500 g.
Still another conventional packaging material for photographic photosensitive materials is, as disclosed in Japanese Utility Model KOKOKU No. 2-736, composed of a porous sheet and uniaxially molecularly oriented polyolefin resin film laminated onto both sides so that respective molecular orientation axes are crossed. The packaging material does not rupture, even when a photographic film having sharp edges and a weight of not less than 500 g is contained. However, the packaging material is expensive, because of requiring two film molding machines for stretching uniaxially for laminating two uniaxially molecularly oriented films in a crossed state and the generation of a great trim loss. Since both inside faces facing each other of a bag are the same uniaxially molecularly oriented film, not only is automatic bag making impossible but also an expensive impulse sealer is necessary due to its inferior heat sealing properties. Moreover, heat sealing part must be covered by a heat-resistant Teflon tape protected from the heating bar of the heat sealer so as not to form pinholes at the boundaries of the heat-sealed part, and the heat-sealed part must be cooled immediately after sealing by cooled water. As a result, thermal efficiency is inferior and increases manufacturing cost. Further problems are in gradual decrease of heat seal strength, the generation of static electricity, surface temperature elevation up to more than 70.degree. C. by leaving under the sunlight, the difficulty in the discrimination of obverse side and reverse side under safety light, and the like.